High impedance electrical testing instrument for AC and DC voltage detection and continuity testing

• US 4,205,264 A
• Filed: 04/25/1978
• Issued: 05/27/1980
• Est. Priority Date: 04/25/1978
• Status: Expired due to Term

• Current Assignee: Charles Gold
• Original Assignee: Charles Gold
• Inventors: Gold, Charles
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US05/899,794
• Time in Patent Office: 763 Days
• Field of Search: 324/51, 324/72.5, 324/133, 324/149, 324/123 R, 324/62
• US Class Current: 324/556
• CPC Class Codes: G01R 19/155 Indicating the presence of voltage
• CPC Class Codes: G01R 31/50 Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections testing of sparking plugs H01T13/58
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults
• CPC Class Codes: G01R 31/54 Testing for continuity

Abstract

An electrical testing instrument including a high gain amplifier circuit having a pair of inputs, one comprising a probe and the other covered at least in part by a non-conductive material and being adapted for manual engagement by the user for completing an input circuit through the body of the user. The circuit has a battery and a current-responsive indicator in its output circuit to provide a signal when current flows in the input circuit to provide a critical forward biasing of the amplifier. The battery is connected to furnish such input current when the input terminals are connected in a closed circuit having a resistance of at least approximately the resistance of the user'"'"'s body. The amplifier circuit is further arranged that when the probe is contacted with a live AC power line and the user engages the portion of the manually engageable input terminal which is covered with a non-conductive material, an operating indicating current will also be present in the output circuit.

Claims

1. An electric testing instrument comprising:

a housing having a wall of electrically conductive material adapted for manual engagement by the user and forming an input terminal for completion of an input circuit through the body of the user;

an amplifier mounted in said housing and having its input connected to an input circuit comprising a probe providing a second input terminal adapted for engagement with an electric signal, said amplifier having an output circuit comprising in series a collector, an emitter, a battery and a current responsive indicator;

said housing wall being connected to the side of said battery connected to said collector and having polarity opposite said emitter;

said indicator providing a manually discernible signal at and above an operating current flow in said output circuit, said amplifier having a gain sufficient to provide said operating current flow in said output circuit when said input circuit is biased with an input current;

said input circuit providing said input current derives solely from said battery when said input terminals are connected across a resistance from zero ohms to as high as at least one megohm;

an electrically nonconductive material covering a portion of said housing wall;

said amplifier having a sufficient gain to provide said operating output current flow when said probe is connected to a conventional live power line providing approximately 110 volts a.c. and said nonconductive material is manually engaged by the user; and

said material covering a part only of said wall leaving an uncovered portion for direct manual engagement by the user for through the body continuity testing and for detecting the presence of d.c. voltage, thereby enabling the user to distinguish between a.c. and d.c. signals.